The present invention relates generally to an image reproducing apparatus, and more particularly to an apparatus for reproducing an image by coding supplementary digital signals together with image signals through a transform coding process, the apparatus having capabilities of inputting and outputting digital signals for carrying out a text/image composition process and a text/image separation process.
Conventionally, there is a technique for coding a supplementary digital signal together with an image signal so as to compress the range of data to a narrower range, and for decoding the resulting combined signal. The image signal can be a facsimile signal which exhibits a high degree of correlation. The digital signal can represent any other data which is independent of the image signal. For example, U.S. Pat. No. 4,237,484 discloses such a technique. There is also a text/image composition technique for combining text data with a halftone image signal by using a prescribed discrete orthogonal transform process. In this technique, a redundant portion of image data produced after the transform process is performed is replaced by the text data, the resulting image data containing the text data being encoded into coded information which have a form of a matrix of blocks in orthogonal transform coordinates. The redundant portion, which includes frequency components produced when the transform coding process is performed, is used for combining the text data with the halftone image data, and only a small quantity of text data can be combined with the halftone image data without seriously degrading the picture quantity.
However, in the above mentioned techniques, no preprocessing of the supplementary digital signals is performed, and the quantity of the digital signals to be combined with the image signals is limited and not reduced to a narrower range so that a large quantity of supplementary digital signals cannot be combined with the image signals without degrading the picture quality. Thus, there is a problem in that it is difficult to reproduce an image containing a large quantity of text data combined with image signals without seriously degrading the picture quality.